Controller for reducing power

Abstract

A controller includes a microcomputer that operates in a normal mode or in a low power mode and communicates with an external device, a monitor circuit that monitors an operation state of the microcomputer based on a monitor signal output from the microcomputer, and a start circuit that controls a drive of the monitor circuit. Communication signals exchanged between the microcomputer and the external device include a dominant state and a recessive state, and the start circuit monitors the communication signals. When the communication signals in the low power mode of the microcomputer include the dominant state, the start circuit puts the monitor circuit in a monitoring state. When no monitor signal is input from the microcomputer to the monitor circuit that is operating in the monitoring state, the monitor circuit determines that an abnormality has occurred in the microcomputer.

What is claimed is: 
     
       1. A controller comprising:
 a microcomputer operating in a normal operation mode and a low power consumption mode consuming less electric power than the normal operation mode and communicating with an external device; 
 a monitor circuit monitoring an operation state of the microcomputer; and 
 a start circuit controlling a drive of the monitor circuit, wherein 
 the microcomputer generates and outputs a pulse shape monitor signal in the normal operation mode to the monitor circuit, the pulse shape monitor signal indicating that the operation state of the microcomputer is normal, 
 the monitor circuit monitors the operation state of the microcomputer based on the monitor signal, 
 pulse shape communication signals exchanged for communication between the microcomputer and the external device are in a dominant state or a recessive state, the dominant state of a communication signal indicating that the communication signal is a signal of significance and the recessive state of the communication signal being continuously output when the communication is stopped, 
 the start circuit monitoring the pulse shape communication signals puts the monitor circuit in a monitoring state when the pulse shape communication signals in the low power consumption mode of the microcomputer include the dominant state, and 
 the monitor circuit in the monitoring state determines that an abnormality has occurred in the microcomputer when no monitor signal is input to the monitor circuit. 
 
     
     
       2. The controller of  claim 1 , wherein
 when the microcomputer is in the low power consumption mode and the communication signals include the dominant state, the start circuit (i) outputs a start signal to the microcomputer, the start signal instructing an execution of a start process for a transition of the microcomputer from the low power consumption mode to the normal operation mode, and (ii) puts the monitor circuit in the monitoring state, and 
 when the monitor circuit in the monitoring state receives no monitor signal for at least a start process time that is required for completing the start process of the microcomputer from an output of the start signal to the microcomputer, the monitor circuit determines that that the abnormality has occurred in the microcomputer. 
 
     
     
       3. The controller of  claim 2  further comprising:
 an output circuit outputting a control signal from the microcomputer to an external element; and 
 a power circuit supplying a drive voltage to the output circuit, wherein 
 the microcomputer in the normal operation mode controls an operation of the external element by outputting the control signal to the external element as well as communicating with the external device, 
 a supply of the drive voltage to the output circuit is controlled by a power signal that is output from the microcomputer to the power circuit, and 
 the start circuit puts the monitor circuit in the monitoring state based at least on one of the communication signal and the power signal. 
 
     
     
       4. The controller of  claim 3 , wherein
 the start circuit puts the monitor circuit in the monitoring state when the supply of the drive voltage to the output circuit is enabled based on the power signal, and 
 when the monitor circuit in the monitoring state receives no monitor signal, the monitor circuit determines that the abnormality has occurred in the microcomputer. 
 
     
     
       5. The controller of  claim 2 , wherein
 the microcomputer generates and outputs the monitor signal to the monitor circuit when operating in the normal operation mode, and when performing an end process of the microcomputer for a transition from the normal operation mode to the low power consumption mode, 
 the start circuit puts the monitor circuit in the monitoring state when the microcomputer is performing the end process, and 
 the monitor circuit determines that the abnormality has occurred in the microcomputer when the monitor circuit receives no monitor signal. 
 
     
     
       6. The controller of  claim 5 , wherein
 the start circuit puts the monitor circuit in the monitoring state when the microcomputer is operating in the normal operation mode, and 
 the monitor circuit determines that the abnormality has occurred in the microcomputer when the monitor circuit receives no monitor signal. 
 
     
     
       7. The controller of  claim 6 , wherein
 the microcomputer generates a state signal that indicates that the microcomputer is either in the normal operation mode or in the low power consumption mode, and 
 the start circuit determines the operation state of the microcomputer based on the state signal. 
 
     
     
       8. The controller of  claim 7 , wherein
 when the microcomputer is performing the end process, the microcomputer generates the state signal that indicates that the microcomputer is in the normal operation mode. 
 
     
     
       9. The controller of  claim 7 , wherein
 when the microcomputer is performing the start process, the microcomputer generates the state signal that indicates that the microcomputer is in the low power consumption mode. 
 
     
     
       10. The controller of  claim 7 , wherein
 the monitor circuit maintains the monitoring state (i) during a start period from a monitor start time when the monitor circuit inputs the start signal to the microcomputer and switches during the monitoring state to a state signal reception time when the state signal that indicates that the microcomputer is in the normal operation mode is output from the microcomputer to the monitor circuit or (ii) during a first preset period that is equal to or longer than an expected start period. 
 
     
     
       11. The controller of  claim 10 , wherein
 when the monitor circuit determines that the abnormality has occurred in the microcomputer, the monitor circuit outputs a reset signal to the microcomputer for controlling the microcomputer to perform the start process. 
 
     
     
       12. The controller of  claim 11 , wherein
 the monitor circuit maintains the monitoring state (i) during a reset period from an output of the reset signal from the monitor circuit to the microcomputer to an output of the state signal from the microcomputer to the monitor circuit, the state signal indicative of the microcomputer being in the normal operation mode, or (ii) during a second preset period that is equal to or longer than an expected reset period. 
 
     
     
       13. The controller of  claim 7  further comprising:
 a communication circuit communicating with the external device, wherein 
 the microcomputer performs communication with the external device via the communication circuit, 
 the communication circuit operates in the normal operation mode or in the low power consumption mode, 
 the communication circuit in the low power consumption mode transits to the normal operation mode when the communication signals that are output from the external device include the dominant state, and 
 the communication circuit in the normal operation mode transits to the low power consumption mode when the state signal that indicates that the microcomputer is in the low power consumption mode is input to the communication circuit. 
 
     
     
       14. The controller of  claim 1 , wherein
 the microcomputer does not generate and does not output the pulse shape monitor signal in the low power consumption mode to the monitor circuit. 
 
     
     
       15. The controller of  claim 1 , wherein
 the microcomputer communicates with the external device over the Local Interconnect Network.